1. Field of the Invention
The present invention relates to a rotating electric machinery which reduces noise.
2. Description of the Prior Art
Heretofore, rotating electric machinery used for an electric car such as a traction motor has a structure shown in FIG. 1, wherein the reference numeral (1) designates a yoke; (2) designates a suction hole formed on the yoke (1); (3) designates an exhaust hole formed on the yoke (1); (4) and (5) respectively designate end brackets formed at each end of the yoke (1); (6) designates a bearing formed on each end bracket (4), (5); (7) designates a shaft supported by the bearing (6); (8) designates a rotor consisting of an iron core, a coil and a commutator connected to a spider (9); (10) designates an air-passage formed in the rotor (8) and the rotor spider (9); (11) designates a fan fixed on the shaft (7); (12) designates a brush device equipped with the end bracket (5) to contact with the commutator; and (13) designates a stator consisting of an iron core formed on the yoke (1) and a coil.
In the motor having the aforementioned structure, the fan (11) is driven depending upon the rotation of the rotor (8) whereby the air sucked from the air suction hole (2) is passed through the space between the rotor (8) and the stator (13) and the air passage (10) as shown by the broken arrow line to cool the heated rotor (8) and the stator (13). The air heated by the cooling said rotor and stator, is discharged through the exhaust hole (3) by the rotating fan (11).
The traction motor for an electric car is usually driven in a range of 0 to 4000 r.p.m. In the conventional traction motor, the fan (11) is fixed on the shaft (7). Therefore, the fan (11) rotates at the same revolving speed as that of the traction motor as shown by the broken line in FIG. 2. The noise caused in the revolving of the traction motor increases depending upon an increase of the revolving speed as shown by the broken line in FIG. 3. The main factor of the noise is considered as an air blow sound caused by the fan (11). In the conventional traction motor, the following relation is given; ##EQU1##
The conventional traction motor has the disadvantage that the noise increases depending upon the increase of the revolving speed.